Search for the b --> d gamma process

TL;DR

This paper reports a search for the rare b --> d gamma decay process in B mesons, setting an upper limit on its branching fraction to constrain CKM matrix elements, with no significant signal observed.

Contribution

First search for the b --> d gamma process using a large B meson sample, establishing an upper limit on its branching fraction.

Findings

No significant signal detected for the decay modes.

Upper limit on the combined branching fraction set at 1.4 x 10^-6.

Results constrain the ratio |Vtd/Vts| in the CKM matrix.

Abstract

We report the results of a search for the flavor-changing neutral current process b --> d gamma using a sample of 275 million B meson pairs accumulated by the Belle detector at KEKB. We find no significant signal for the exclusive decays B- --> rho- gamma, B0B --> rho0 gamma, or B0B --> omega gamma. Assuming an isospin relation between the three modes, we set an upper limit for the combined branching fraction Br(B --> (rho,omega) gamma) < 1.4 x 10-6 at the 90% confidence level. This limit can be used to constrain the ratio of CKM matrix elements |Vtd/Vts|.